The present invention relates to the manufacturing of semiconductor devices, and more particularly, to a dual inlaid structure.
The escalating requirements for high density and performance associated with ultra large scale integration (ULSI) semiconductor device wiring are difficult to satisfy in terms of providing sub-micron-sized, low resistance-capacitance (RC) metallization patterns. This is particularly applicable when the sub-micron-features, such as vias, contact areas, lines, trenches, and other shaped openings or recesses have high aspect ratios (depth-to-width) due to miniaturization.
Conventional semiconductor devices typically comprise a semiconductor substrate, usually of doped monocrystalline silicon (Si), and a plurality of sequentially formed inter-metal dielectric layers and electrically conductive patterns. An integrated circuit is formed therefrom containing a plurality of patterns of conductive lines separated by inter-wiring spacings, and a plurality of interconnect lines, such as bus lines, bit lines, word lines and logic interconnect lines. Typically, the conductive patterns of vertically spaced metallization levels are electrically interconnected by vertically oriented conductive plugs filling via holes formed in the inter-metal dielectric layer separating the metallization levels, while other conductive plugs filling contact holes establish electrical contact with active device regions, such as a source/drain region of a transistor, formed in or on a semiconductor substrate. Conductive lines formed in trench-like openings typically extend substantially parallel to the semiconductor substrate. Semiconductor devices of such type according to current technology may comprise five or more levels of metallization to satisfy device geometry and microminiaturization requirements.
A commonly employed method for forming conductive plugs for electrically interconnecting vertically spaced metallization levels is known as xe2x80x9cdamascenexe2x80x9d or xe2x80x9cinlaidxe2x80x9d-type processing. Generally, this process involves forming a via opening in the inter-metal dielectric layer or interlayer dielectric (ILD) between vertically spaced metallization levels. The via opening is subsequently filled with metal to form a via electrically connecting the vertically spaced apart metal features. The via opening is typically formed using conventional lithographic arid etching techniques. After the via opening is formed, the via is filled with a conductive material, such as tungsten (W), using conventional techniques, and the excess conductive material on the surface of the inter-metal dielectric layer is then typically removed by chemical mechanical planarization (CMP).
A variant of the above-described process, termed xe2x80x9cdual inlaidxe2x80x9d processing, involves the formation of an opening having a lower contact or via opening section which communicates with an upper trench section. The opening is then filled with a conductive material to simultaneously form a contact or via in contact with a conductive line. Excess conductive material on the surface of the inter-metal dielectric layer is then removed by CMP. An advantage of the dual inlaid process is that the contact or via and the upper line are formed simultaneously.
High performance microprocessor applications require rapid speed of semiconductor circuitry, and the integrated circuit speed varies inversely with the resistance and capacitance of the interconnection pattern. As integrated circuits become more complex and feature sizes and spacings become smaller, the integrated circuit speed becomes less dependent upon the transistor itself and more dependent upon the interconnection pattern. If the interconnection node is routed over a considerable distance, e.g., hundreds of microns or more, as in submicron technologies, the interconnection capacitance limits the circuit node capacitance loading and, hence, the circuit speed. As integration density increases and feature size decreases, in accordance with submicron design rules, the rejection rate due to integrated circuit speed delays significantly reduces manufacturing throughput and increases manufacturing costs.
Copper (Cu) and Cu-based alloys are becoming increasingly attractive for use in VLSI and ULSI semiconductor devices, which require multi-level metallization levels. Cu and Cu-based alloy metallization systems have very low resistivities which are significantly lower than W and even lower than those of previously preferred systems utilizing Al and its alloys. Additionally, Cu has a higher resistance to electromigration. Furthermore, Cu and its alloys enjoy a considerable cost advantage over a number of other conductive materials, notably silver (Ag) and gold (Au). Also, in contrast to Al and refractory-type metals (e.g., titanium (Ti), tantalum (Ta) and W), Cu and its alloys can be readily deposited at low temperatures formed by well-known xe2x80x9cwetxe2x80x9d plating techniques, such as electroless and electroplating techniques, at deposition rates fully compatible with the requirements of manufacturing throughput.
Another technique to increase the circuit speed is to reduce the capacitance of the inter-metal dielectric layers. Dielectric materials such as silicon oxide (SiO2) have been commonly used to electrically separate and isolate or insulate conductive elements of the integrated circuit from one another. However, as the spacing between these conductive elements in the integrated circuit structure has become smaller, the capacitance between such conductive elements because of the dielectric being formed from silicon oxide is more of a concern. This capacitance negatively affects the overall performance of the integrated circuit because of increased power consumption, reduced speed of the circuitry, and cross-coupling between adjacent conductive elements.
A response to the problem of capacitance between adjacent conductive elements caused by use of silicon oxide dielectrics has led to the use of other dielectric materials, commonly known as low-k dielectrics. Whereas silicon oxide has a dielectric constant of approximately 4.0, many low-k dielectrics have dielectric constants less than 3.5. Examples of low-k dielectric materials include organic or polymeric materials. Another example is porous, low density materials in which a significant fraction of the bulk volume contains air, which has a dielectric constant of approximately 1. The properties of these porous materials are proportional to their porosity. For example, at a porosity of about 80%, the dielectric constant of a porous silica film, i.e. porous SiO2, is approximately 1.5.
A problem associated with the use of many low-k dielectric materials is that these materials can be damaged by exposure to oxidizing or xe2x80x9cashingxe2x80x9d systems, which remove a resist mask used to form openings, such as vias, in the low-k dielectric material. This damage can cause the surface of the low-k dielectric material to become a water absorption site, if and when the damaged surface is exposed to moisture. Subsequent processing, such as annealing, can result in water vapor formation, which can interfere with subsequent filling with a conductive material of a via/opening or a inlaid trench formed in the dielectric layer. For this reason, the upper surface of the low-k dielectric material is typically protected from damage during removal of the resist mask by a capping layer, such as silicon oxide, disposed over the upper surface.
A number of different variations of an inlaid process using low-k dielectrics have been employed during semiconductor manufacturing.
FIGS. 1A-1J depict a first dual inlaid process for forming vias and a second metallization level over a first metallization level, according to conventional techniques.
In FIG. 1A, a first etch stop layer 12 is deposited over a first metallization level 10. The first etch stop layer 12 acts as a passivation layer that protects the first metallization level 10 from oxidation and contamination and prevents diffusion of material from the first metallization level 10 into a subsequently formed dielectric layer. The first etch stop layer 12 also acts as an etch stop during subsequent etching of the dielectric layer. A typical material used as an etch stop is silicon nitride, which may be deposited by PECVD.
In FIG. 1B, a first dielectric layer 14 is deposited over first etch stop layer 12, typically by spinning a liquid dielectric material onto the first etch stop layer 12 surface under ambient conditions to a desired depth. This is typically followed by a heat treatment to evaporate solvents present within the liquid dielectric material and to cure the film to form the dielectric layer 14.
In FIG. 1C, a second etch stop layer 40, also known as a middle stop layer or hard mask layer, is deposited over the first dielectric layer 14. The second etch stop layer 40 acts as an etch stop during etching of a dielectric layer subsequently formed over the second etch stop layer 40. As with the first etch stop layer 12, the second etch stop layer 40 may comprise a silicon nitride or silicon oxynitride deposited by PECVD. A via pattern 41 is etched into the second etch stop layer 40 using conventional photolithography and appropriate anisotropic dry etching techniques, such as an O2 or (H2+N2) etch. These steps are not depicted in FIG. 1C and only the resulting via pattern 41 is depicted therein. The photoresist used in the via patterning is removed by an oxygen plasma, for example.
In FIG. 1D, a second dielectric layer 42 is deposited over the second etch stop layer 40. After formation of the second dielectric layer 42, a capping layer or hard mask 13 can be formed over the second dielectric layer 42. The function of the capping layer 13 is to protect the second dielectric layer 42 from the process that removes a subsequently formed resist layer. The capping layer 13 can also be used as a mechanical polishing stop to prevent damage to the second dielectric layer 42 during subsequent polishing away of conductive material that is deposited over the second dielectric layer 42 and in a subsequently formed via and trench. Examples of materials used as a capping layer 13 include silicon oxide and silicon nitride.
In FIG. 1E, the pattern of the trenches are formed in the capping layer 13 using conventional lithographic and etch techniques. The lithographic process involves depositing a resist 44 over the capping layer 13 and exposing and developing the resist 44 to form the desired pattern of the trench. The first etch, which is an anisotropic etch highly selective to the material of the capping layer and exposed portions of the resist 44, such as a reactive ion plasma dry etch, removes the exposed portions of the resist and underlying exposed portions of capping layer 13.
In FIG. 1F, a second etch, which is highly selective to the material of the first dielectric layer 14 and second dielectric layer 42, anisotropically removes the dielectric material until the first etch stop layer 12 is reached. In this way, a trench 50 and via 51 are formed in the same etching operation. The second etch is typically an anisotropic etch, such as a reactive ion plasma dry etch, that removes only the exposed portions of the first low-k dielectric layer 14 directly below the opening in the second etch stop layer 40 and the exposed portions of the low-k dielectric materials. By using an anisotropic etch, the via 51 and the trench 50 can be formed with substantially perpendicular sidewalls.
The thickness of the trench photoresist is selected to be completely consumed by the end of the etch operation, to eliminate the need for photoresist stripping. This results in the structure depicted in the top portion of FIG. 1G, wherein all of the photoresist has been stripped. Another etch, which is highly selective to the material of the first etch stop layer 12, then removes the portion of the etch stop layer 12 underlying via 51 until the etchant reaches the first metallization level 10. This etch is also typically a dry anisotropic etch chemistry designed not to attack any other layers in order to expose a portion of the metallization.
In FIG. 1H, an adhesion/barrier material, such as tantalum, titanium, tungsten, tantalum nitride, or titanium nitride, is deposited. The combination of the adhesion and barrier material is collectively referred to as a diffusion barrier layer 20. The diffusion barrier layer 20 acts to prevent diffusion into the first and second dielectric layers 14, 42 of the conductive material subsequently deposited into the via 51 and trench 50.
In FIG. 11, a layer 22 of a conductive material for example, a Cu or Cu-based alloy, is deposited in the via 51 and trench 50 and over the capping layer 13. A typical process initially involves depositing a xe2x80x9cseedxe2x80x9d layer on the barrier layer 20 subsequently followed by conventional plating techniques, e.g., electroless or electroplating techniques, to fill the via 51 and trench 50. So as to ensure complete filling of the via 51 and trench 50, the Cu-containing conductive layer 22 is deposited in trench 50 and via 51 and over the upper surface of the capping layer 13.
In FIG. 1J, the entire excess thickness of the metal overburden layer 24 over the upper surface of the capping layer 13 is removed using a CMP process. A typical CMP process utilizes an alumina (Al2O3)-based slurry, which leaves a conductive plug in the via 51 and a second metallization level in the trench 50. The second metallization level has an exposed upper surface which is substantially co-planar with the upper surface of the capping layer 13.
One problem associated with the above-identified process is overlay error. Since integrated circuits are fabricated by patterning a plurality of layers in a particular sequence to generate features that require a particular spatial relationship with respect to one another, as shown in FIGS. 1A-1J, above, each layer must be properly aligned with respect to previously patterned layers to minimize the size of individual devices and thus maximize the packing density on the substrate. A perfect overlap is not easily achieved and some misalignment is common. Excessive misalignment between successive masks used in the manufacture of the semiconductor integrated circuit can produce an overlay error that may ultimately result in the failure of the circuit to operate properly. For example, this overlay error may cause a reduction in the final via size with a corresponding increase in via resistance. Therefore, an overlay tolerance or overlay xe2x80x9cbudgetxe2x80x9d, as defined by the particular tools and processes employed, is required between two layers to ensure reliability in the construction of the resulting device.
An example of overlay error in the fabrication of a dual inlaid semiconductor structure in accord with the above process is depicted in plan view in FIG. 2A and in cross-section in FIGS. 2B and 2C. FIG. 2A shows a step in the fabrication process wherein a trench 200 is etched to reach a previously formed via hole pattern 250. FIG. 2B depicts in cross-section trench pattern 200, resist layer 202, hard mask layer 204, dielectric layer 206, middle stop layer 208, dielectric layer 210, etch stop layer 212, metallization layer 214, and via hole pattern 250. This structure, and the method for forming the structure, comports with the method and structure for forming a dual inlaid structure, discussed above, and a detailed discussion is therefore omitted. As shown, an overlay error exists between the via hole pattern 250 formed in middle stop layer 208 and the trench pattern 200 formed in hard mask layer 204. Upon formation of a trench and a via hole, in a manner as described above, the width of the resulting via contact W2 is less than the intended width W1. To overcome this problem, an overlay budget is conventionally applied to the via hole pattern 250 wherein approximately half of the overlay budget is applied to each side of the via hole pattern 250 width. However, this process requires numerous steps to form the dual inlaid structure and is complex.
Another conventional dual inlaid process for forming vias and a second metallization level over a first metallization level is shown in FIGS. 3A-3D.
In FIG. 3A, an etch stop layer 310 comprising a suitable etch stop material, such as silicon nitride, is deposited over a metallization level 300. The etch stop layer 310 acts as a passivation layer that protects the metallization level 300 from oxidation and contamination and prevents diffusion of material from the metallization level 300 into a subsequently formed dielectric layer. The etch stop layer 310 also acts as an etch stop during subsequent etching of the dielectric layer. A dielectric layer 320 is deposited over etch stop layer 310. The dielectric layer may comprise a conventional dielectric or a low-k dielectric material. A hard mask layer 330 is deposited over dielectric layer 320 and may comprise, for example, a silicon carbide or silicon oxynitride. A resist 340 is deposited over hard mask layer 330.
As shown in FIG. 3B, a trench pattern 355 is lithographically formed in the resist 340 using conventional photolithography and appropriate anisotropic dry etching techniques. These steps are not depicted in FIG. 3B, and only the resulting structures are depicted. The patterning of resist 340 may be enhanced by use of an antireflective hard mask layer 330, such as silicon oxynitride. Portions of the hard mask layer 330 exposed by removing the exposed portions of the resist are then etched using conventional etching methods.
In FIG. 3C, the trench 360 is formed by anisotropically etching through dielectric layer 320 to an appropriate depth, determined by use of a closely timed etch. Alternatively, a middle stop layer (not shown) could be used. Subsequently, resist 340 used in the trench patterning is removed by an oxygen plasma, for example, and another resist 370 is applied over the hard mask layer 330 and trench 360.
As shown in FIG. 3D, a via 390 is formed using conventional photolithography and appropriate anisotropic dry etching techniques. These steps are not depicted in FIG. 3D, and only the resulting structure of the selective anisotropic etch of resist 370, dielectric layer 320, and etch stop layer 310 is shown. Subsequent to formation of the via 390 and trench 360, the resist 370 is removed and an adhesion/barrier material (not shown) is formed in the via 390 and trench 360. A conductive material such as Cu or Cu-based alloy is then deposited over the via 390 and trench 360, followed by chemical mechanical polishing.
However, the dual inlaid process illustrated in FIGS. 3A-3D patterns the via over a substantial step, which seriously degrades pattern fidelity due to the different thicknesses across the surface causing, for example, significant light scatter. Thus, lithography is made more difficult. Accordingly, a need exists for a method of forming a dual inlaid structure while minimizing the aforementioned disadvantages of conventional dual inlaid schemes and a need exists for a simplified dual inlaid scheme that minimizes a required number of process steps to form the dual inlaid structure.
The need in the art for a simplified method of forming a dual inlaid structure which accounts for overlay error and minimizes the required number of steps while overcoming some of the deficiencies of the conventional dual inlaid techniques is met by embodiments of the present invention.
These embodiments provide, in one aspect, a method of manufacturing a semiconductor structure including etching an opening in a hard mask layer including a trench pattern with a first portion having a first width and a second portion being an oversized trench portion having a second width greater than a width of the first portion, the second portion being formed over a predetermined via location. Also included are steps of depositing a resist and patterning a via pattern in the predetermined via location, etching a via corresponding to the via pattern through the resist and at least partially through a dielectric layer, and etching an oversized trench portion corresponding to the second portion opening in the hard mask.
In another aspect, the invention includes a method of manufacturing a semiconductor device including the steps of sequentially forming a metallization layer, an etch stop layer, a dielectric layer, and a hard mask layer, followed by etching an opening in a hard mask layer including a trench pattern with a first portion having a first width and a second portion being an oversized trench portion having a second width greater than a width of the first portion, the second portion being formed over a predetermined via location. The method also includes depositing a resist and patterning a via pattern in the predetermined via location, etching a via corresponding to the via pattern through the resist and at least partially through a dielectric layer; and etching an oversized trench portion corresponding to the oversized opening in the hard mask. In this aspect of the invention, an overlay budget is applied to each side of the oversized trench portion pattern across a width of the oversized trench portion pattern and to each side of the oversized trench portion pattern along E length of the oversized trench portion pattern.
In still another aspect, the invention includes a semiconductor device including at least one dielectric layer, a trench formed in the dielectric layer including a first portion having a first width and a second portion being an oversized trench portion having a second width greater than the first width of the first portion, wherein the second portion overlies a predetermined via location. A via is formed in the dielectric layer substantially in or adjacent the predetermined via location and circumferential edges of the oversized trench portion are displaced from corresponding edges of the via opening by at least a predetermined overlay budget.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.